Anyone have experience wiring up the factory battery gauge in a 1972 C10? I recently did a swap out from idiot lights to factory gauges, now everything works but the batt gauge.

I can't understand how these old batt. gauges operate. They basically have two hot wire hookups, one from the positive battery (passenger fender junction) and one from the red hotwire off the back of the alternator, at dash clip wires 12 and 1, respectively. I've been told the gauge measures the difference in amperage between the two. However, two hotwires don't make a circuit...there is no ground, except dash clip wire #7, which is seperate. But if you hook the gauge between positive battery and ground, you smoke the gauge.

Is there supposed to be a resistor or jumper across the back of the gauge? Mine just has this piece of varnished-looking cardboard. Also, I get continuity across both posts in the back. Does that mean the gauge is shorted, or is that the way it's supposed to be? Looks like the gauge is nothing but some fine copper wire wound around a chunk of plastic, soldered to each back post.

i also have same problem but did learn something related. if you have an external voltge regulator system, it needs the gen light bulb in the old dash panel or wont charge. the bulb is part of the circuit. i had to hook up the brown wire from old panel to #5 on the new panel. this will now be connected to temp light, but will allow charging system to work.

I do have a voltage regulator mounted on the truck front clip frame. And the factory wiring diagrams show this is correct.

Also, it looks like there is a brown or brown/white wire from the ignition switch that ties in with the old brown generator light wire in the fusebox sandwich plug on the firewall.

OK, so let me clarify this. You swapped from idiot lights to factory gauges, and in order for your batt gauge to work you had to run the brown wire from the old dash clip wire #8 to the new dash clip wire #5? Because #5 on my diagram:http://www.gmcpaulstruckparts.com/Tech%20Tips1.htm is not used (blank), just like in the idiot light dash wire #3 wasn't used.

Also, the temp gauge wire is #6 not #5, so I'm a little confused still on your reply.

It's an external shunt type ammeter it doesn't really measure amps it is more of a charge indicator. The charge wire is the shunt in the system and the gauge is connected at either end of the wire and is calibrated to the wires resistance make sure you fuse both wires (3-4 amp). When the ammeter sees x voltage on the battery end of the shunt (wire) it expects x voltage on the alt. end because of the shunts fixed resistance and depending on the voltage differential the ammeter moves accordinly. On smaller GM cars there was an actual shunt installed the pic below is a shunt from a chevyII.

it is confusing. #5 on the new panel isnt used because it goes to a temp light. #6 is for the temp guage. a light bulb is reqired for the old external regulator to work. the new panel doesnt have a gen light, but does have a temp light that isnt used so i hooked it up there. now my system charges. as far as the charge guage i havent figured it out yet. to me you are hooking up both leads on guage to the same wire, 3 feet apart. i dont see a voltage difference.

Also, it looks like there is a brown or brown/white wire from the ignition switch that ties in with the old brown generator light wire in the fusebox sandwich plug on the firewall.

IIRC It's either or not both the brown/white wire from the ignition switch is for the gauge set up and it has a built in resistance (10 ohm) Delco recomends on models with a gen light that the reisistor wire be installed parallel to the gen light circuit but I don't think GM did this. So simply connect the existing brown wire to an ignition source but you'll have to add a 10 ohm resistor.

it is confusing. #5 on the new panel isnt used because it goes to a temp light. #6 is for the temp guage. a light bulb is reqired for the old external regulator to work. the new panel doesnt have a gen light, but does have a temp light that isnt used so i hooked it up there. now my system charges. as far as the charge guage i havent figured it out yet. to me you are hooking up both leads on guage to the same wire, 3 feet apart. i dont see a voltage difference.

Thats a really good idea if you connect it to pin 5 you wont need to add a resistor (bulb provides the needed resistance) and you'll have a second charge indicator. The charge wire at 30 amps will drop the voltage ~.5 volts and the gauge is a presision instument that can detect these small changes in current.

I am with you. How can a guage read current difference between 2 essentially the same hotwires (batt positive & alt. red hot wire) 3 feet apart? Two hotwires never complete any kind of circuit, it seems a ground should be somewhere...but these little mickey mouse gauges go up in smaoke if you ciomplete them in a 12v DC circuit.

Your gauge cluster needs be grounded for all the lights to work. Forget the resistor go with Neba's suggestion and move the brown wire to pin # 5 it's cleaner. The fuses are there to protect the printed circuit board IDK if it can handle 5 amps it probably can but dont know for sure

I just ran a wire from the old generator light wire (it was twinned with the brown/white wire from the ignition clip) to pin #5 in the dash clip (originally not used for anything) and fired up the old beast. Not so much as a twitch out of the battery gauge.

Sounded too good to be true...and was, at least for me! Back to the drawing board.

BTW, does anyone know if you are suppossed to get continuity across the two copper posts on the backside of the battery gauge? Mine ohms out, and I'm wondering if that means the gauge is shorted out, or if that is what it is suppossed to do.

ok, i gave up on trying to get the charge guage to work and will install an aftermarket guage under the dash. what i was trying to say was your charging system wont work if you have an external voltage regulator and switch from idiot light panel to guage panel.

You're saying basically that your alternator won't charge your battery if you do the dash switch unless you run the extra wire to pin #5 in the dash clip? That's pretty weird considering the alt/ hotwire is spliced into the battery positive wire run from the passenger side fender to just below the voltage regulator.

However, mine is now installed and doesn't seem to be hurting anything, so I'll leave it be just in case!

I actually have the book with the "factory" wiring diagrams, and I'm telling you the way this gauge is hooked up makes no sense whatsoever. Basically you have two hot wires run right into the dash clip at pins #1 & #12. One goes to the battery positive wire fender bolt, the other is from the alternator hotwire spliced together in a 5-wire splice by the voltage regulator.

Here's a poll question:

Does anyone have, or has anyone ever seen one of these factory gauges that actually works?

Fixit, I'd be interested to hear from you regarding the shunt system wiring from the old Chevy II's. Maybe there is a way to use that wiring scheme to properly wire these C-10 battery gauges.

You're saying basically that your alternator won't charge your battery if you do the dash switch unless you run the extra wire to pin #5 in the dash clip? That's pretty weird considering the alt/ hotwire is spliced into the battery positive wire run from the passenger side fender to just below the voltage regulator.

However, mine is now installed and doesn't seem to be hurting anything, so I'll leave it be just in case!

I actually have the book with the "factory" wiring diagrams, and I'm telling you the way this gauge is hooked up makes no sense whatsoever. Basically you have two hot wires run right into the dash clip at pins #1 & #12. One goes to the battery positive wire fender bolt, the other is from the alternator hotwire spliced together in a 5-wire splice by the voltage regulator.

Here's a poll question:

Does anyone have, or has anyone ever seen one of these factory gauges that actually works?

Fixit, I'd be interested to hear from you regarding the shunt system wiring from the old Chevy II's. Maybe there is a way to use that wiring scheme to properly wire these C-10 battery gauges.

Your book is correct. You will have to supply the battery gauge wires and fuse them with 4 amp fuses like Fixitp said. You cannot use the no. 5 terminal as there is nothing connected to it on the gauge panel. The no, 1 and 12 terminals are for the battery gauge as you know and you will have to add them to your harness as you also know.

In order for the alternator to charge you will have to add a wire( brown ) to your harness from the ignition switch to the voltage regulator with a 30 ohm resister wired in series. That can be a light but if it blows while you're on the road then the alternator won't charge. It will also be on all the time when the engine is running.
I have added some diagrams for clarity. They show the dash wiring for both systems. The last one is the wiring for the old ammeter with the internal shunt, not sure what type the chevy II used.

The diagram of the old shunt system makes sense to me, whereas the original factory diagram for the C-10 does not. Also, your diagram lacks a voltage regulator, which is critical in the C-10 setup.

It seems that the C-10 guage is probably designed to work the same way, but minus the grounded shunt.

It seems the charging problem stems from the brown wire change-over on the gauge dashes. Basically, there is nowhere for it to go on the new setup. I cut mine off, but then retied back into it and pinned it at #5 in the dash clip, which may not be helpful at all.

I already have a brown wire from the voltage regulator (circuit #25) to the firewall sandwich plug. On the inside firewall plug, there are 2 twinned brown wires. One (brwn/wht) runs to the ignition clip and is twinned with a larger brown wire that runs to the fusebox (4A). The other is now the one I have at pin #5 in the dash clip.

So where are you saying to hook up the original brown wire (old gen. light) from #8 (idiot light) pin in the new gauge system? Are you saying solder in a resistor to this wire and run it back to the voltage regulator (twin it with brown #25?) instead of pin #5 in the dash clip?

Also, one thing I noticed in the C-10 as well as the old shunt-style diagram is the "fusible link" on the charging wire running from the 5-wire splice to the batt. positive connection on the passenger fender. The wire I have is simply a 12g solid red wire (spliced with a butt-connector) -no fuse, links, shunts, etc. I thought this "fusible link" simply meant an inline fuse was recommended here.

Vette, I thought using teminal 5 was a good idea based on the diagram posted in the faq section of the printed circuit board. It shows a dotted line going from terminal 5 to the ground side of the temp light, without any foot notes I assumed that path as well as the positive side was still on the circuit board, just not being used. I dont have a circuit board to verify if it's there or not and if it isn't thanks for the correction.

72step, The brown wire which went to the alt. light is to excite the alternator and has no direct effect on the ammeter. Earlier I stated that "Delco recomends on models with a gen light that the reisistor wire be installed parallel to the gen light circuit but I don't think GM did this" and you indicated that there is a brown/white wire tied into the brown wire. If thats the case you should be good to go, I cant verify this but you can by checking the brown wire at the voltage regulator for power with the key on only also note the voltage drop to verfiy resistance. Delco recomended this to add redundancy to the chargeing system, if the alt. light ever burned out your charging system would still work not leaving you stranded.

72step, I posted the picture of the ChevyII shunt just to illustrate that a shunt is not just a term used to describe ammeters but that it is an actual component in the system. "electrical shunt - a conductor having low resistance in parallel with another device to divert a fraction of the current". On our trucks GM used the charge wire as the shunt because it was a fixed gauge, fixed length so it had a fixed resistance which is why I asked if you changed the wire either length or gauge would change the resistance of the shunt and effect ammeter operation. With the ChevyII as well as other smaller cars it wasn't practical to use the charge wire because the vehicle was smaller and the electrical system was configured differently and the charge wire was too short (not enough resistance) so they had to use an actual resistor. The diagram below shows the shunt wired parallel with the ammeter so whether it's the shunt or the charge wire it's still parallel with the gauge.

I pulled the plug at the voltage reg. and checked the brown wire: no voltage with the key off. With the key on, it was 12.01 volts (brwn wire to grnd) vs. 12.49 volts at the red wire next to it on the clip to ground. So I guess there is a little resistance, but not much. I've never noticed a charging problem before, but I haven't run the truck much since the dash swap. So although the brown wire to dash pin #5 isn't doing anything, I guess it's not hurting anything either (until someone tells me where it should go!)

As to the charging wire, it is 12g red running from the five wire splice, across the top of the radiator, and finally to the passenger fender/positive batt. junction. However, its not 7', but about 61-62" (5 ft.) from the passenger fender to the 5-wire splice near the volatage regulator.

Does yours have some sort of resistor or current director near the passenger fender/ positive batt bolt? The diagram says "fusible link", but mine is just connected with a butt connector. If current flow is supposed to go from the alternator through the gauge, across the charging wire to the fender bolt/+ batt, and there is no resistor, could voltage be bleeding back through the charging wire, to 5-wire splice, then the gauge, rendering it inoperable?

Vette, I thought using teminal 5 was a good idea based on the diagram posted in the faq section of the printed circuit board. It shows a dotted line going from terminal 5 to the ground side of the temp light, without any foot notes I assumed that path as well as the positive side was still on the circuit board, just not being used. I dont have a circuit board to verify if it's there or not and if it isn't thanks for the correction.

72step, The brown wire which went to the alt. light is to excite the alternator and has no direct effect on the ammeter. Earlier I stated that "Delco recomends on models with a gen light that the reisistor wire be installed parallel to the gen light circuit but I don't think GM did this" and you indicated that there is a brown/white wire tied into the brown wire. If thats the case you should be good to go, I cant verify this but you can by checking the brown wire at the voltage regulator for power with the key on only also note the voltage drop to verfiy resistance. Delco recomended this to add redundancy to the chargeing system, if the alt. light ever burned out your charging system would still work not leaving you stranded.

Pole question, Mine works.

I'm quoting your whole post because you are right in both parts. I have a seven gauge dash that shows the lead from terminal 5 going to the second light from the left which is indeed the temperature light on the three gauge dash. I should have clarified my statement that terminal 5 goes nowhere to read that it goes to the old temperature light but that is not used on the seven gauge dash so the circuit board strip goes there and stops instead of just saying that it doesn't go anywhere. terminal 5 is a ground side terminal on the light so unless it's grounded then the light is useless. I found a dash to illustrate this as you can see the terminal 5 strip to the second light from the left. I can't understand why the conversion isn't working if the pins on the connector are changed and the ammeter wires are added as shown. This conversion has been done dozens of times with good results.

If you think of the battery gauge as what it is it may help. Its a voltmeter that indicates charge or discharge of the battery.

It measures the difference in voltage at 2 points in the charging circuit. One point is close to the battery and the other is close to the alt. If the alt side is higher, indicating the alt is working, the gauge reads toward the right.

This is the same as the shunt resistor discussed above except that GM eliminated the shunt by using the wiring in the truck.

Here's the definition of an external shunt ammeter which is what we have in our trucks.

An external shunt is basically a very low value resistor that is in series just as the ammeter was in the previous example, and then the ammeter is in parallel to the shunt. Basically MOST of the current goes through the shunt and only a small percentage goes through the ammeter. By knowing the resistance of the shunt and the meter, the meter is able to calculate the total current by measuring only the small current that goes through the meter. This kind of setup allows small wires to be run to the ammeter in the cockpit, and the high current to remain in the engine compartment. The danger in these setups on some old cars is there isn't a fuse on that small ammeter wire, So if the shunt is damaged or a connector breaks, it would try to flow all the current through the remaining path which is the small ammeter wire and that would melt that wire (along with whatever else it is next to).

This is the reason there are 2 small fuses in the wiring circuit on our trucks that have battery gauges. They are actually amp meters since they measure amperage differential and not volt meters because there is no connection to the negative side of the circuit.

I can't understand why the conversion isn't working if the pins on the connector are changed and the ammeter wires are added as shown. This conversion has been done dozens of times with good results.

Check Murphy's law X 10 for me.

Quote:

It measures the difference in voltage at 2 points in the charging circuit. One point is close to the battery and the other is close to the alt. If the alt side is higher, indicating the alt is working, the gauge reads toward the right.

Oh mine IS slightly to the right. Pull the whole dash panel out, it's slightly to the right, hook it up, it's slightly to the right, start the truck it's slightly to the right with never so much as a millimeter/quiver of difference no matter if connected, disconnected, started, or killed. I've checked the wiring a dozen times, it's spot on with the manual. I have voltage at the dash clip pins at both #1 & #12 when checked to ground (#7), circuit is good, gauge ohms out right, it's not shorted, etc.

I'm wondering more and more about that innocuos "fusible link" near the passenger fender on the charging wire in the wiring manual, as well as Fixit's comment about the charging wire being a certain length/resistance.

Oh mine IS slightly to the right. Pull the whole dash panel out, it's slightly to the right, hook it up, it's slightly to the right, start the truck it's slightly to the right with never so much as a millimeter/quiver of difference no matter if connected, disconnected, started, or killed. I've checked the wiring a dozen times, it's spot on with the manual. I have voltage at the dash clip pins at both #1 & #12 when checked to ground (#7), circuit is good, gauge ohms out right, it's not shorted, etc.

I'm wondering more and more about that innocuos "fusible link" near the passenger fender on the charging wire in the wiring manual, as well as Fixit's comment about the charging wire being a certain length/resistance.

Well if you check the circuit for the battery gauge wires then you can see they run from the gauge to the fender terminal and from the gauge to the three way connector of the alternator, regulator,and the battery. if you followed this then you should have a working gauge, otherwise it must be a gauge problem. I think you have seen this circuit diagram and if not I can post it for you.